I used to do side loading on iOS for a modded YouTube app (uYou+) but now I just use YouTube in the browser with AdGuard and Vinegar extensions. There’s ways to sideload and auto refresh the certificate that don’t need you to connect the phone to a computer which apparently work pretty well (I used AltStore which was pretty annoying because it doesn’t do that).
Usually I think you just have to enable NSFW on a computer/via the browser for it to work in the app. At least that how it is for Telegram iirc. Generally there shouldn’t be a problem accessing anything.
No idea, the only thing I play on my phone is Shattered Pixel Dungeon and I bought that